Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device includes a substrate having a semiconductor fin, in which the semiconductor fin has a first sidewall and a second sidewall opposite to the first sidewall; an epitaxy structure in contact with the first sidewall of the semiconductor fin; and a spacer in contact with the second sidewall of the semiconductor fin and the epitaxy structure.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims priority to U.S. Provisional Application Ser.No. 62/526,432, filed Jun. 29, 2017, which is herein incorporated byreference.

BACKGROUND

Static Random Access Memory (Static RAM or SRAM) is a semiconductormemory that retains data in a static form as long as the memory haspower. SRAM is faster and more reliable than the more common dynamic RAM(DRAM). The term static is derived from the fact that it doesn't need tobe refreshed like DRAM. SRAM is used for a computer's cache memory andas part of the random access memory digital-to-analog converter on avideo card.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a circuit diagram of a six transistor (6T) SRAM cell.

FIGS. 2A, 3A and 4A are top views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure.

FIGS. 2B, 3B, and 4B are perspective views of area B of FIGS. 2A, 3A and4A. FIGS. 5A, 6A, 7A, 8A, 9A, 10A, 11A, and 12A are perspective views ofarea B of FIG. 4A in the following processes.

FIGS. 2C and 3C are cross-sectional views of line A-A of FIGS. 2A and3A. FIGS. 5B, 6B, 7B, 8B, 9B, 10B, 11B, and 12B are cross-sectionalviews of line A-A of FIG. 4A in the following processes.

FIGS. 13 and 14 are cross-sectional views of a semiconductor device inaccordance with some embodiments of the present disclosure.

FIGS. 15A to 15C are cross-sectional views of a method for manufacturinga semiconductor device at various stages in accordance with someembodiments of the present disclosure.

FIGS. 16 and 17 are cross-sectional views of a semiconductor device inaccordance with some embodiments of the present disclosure.

FIGS. 18A to 18C are cross-sectional views of a method for manufacturinga semiconductor device at various stages in accordance with someembodiments of the present disclosure.

FIG. 19 is cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure will be described with respect to embodiments ina specific context, a static random-access memory (SRAM) formed of finfield effect transistors (FinFETs). The embodiments of the disclosuremay also be applied, however, to a variety of semiconductor devices.Various embodiments will be explained in detail with reference to theaccompanying drawings.

Static random-access memory (SRAM) is a type of volatile semiconductormemory that uses bistable latching circuitry to store bits. Bit in anSRAM is stored on four transistors (PU-1, PU-2, PD-1, and PD-2) thatform two cross-coupled inverters. This memory cell has two stable stateswhich are used to denote 0 and 1. Two additional access transistors(PG-1 and PG-2) are electrically connected to the two cross-coupledinventers and serve to control the access to a storage cell during readand write operations.

FIG. 1 is a circuit diagram of a six transistor (6T) SRAM cell. The SRAMcell 100 includes a first inverter 102 formed by a pull-up transistorPU-1 and a pull-down transistor PD-1. The SRAM cell 100 further includesa second inverter 104 formed by a pull-up transistor PU-2 and apull-down transistor PD-2. Furthermore, both the first inverter 102 andsecond inverter 104 are coupled between a voltage bus Vdd and a groundpotential Vss. In some embodiment, the pull-up transistor PU-1 and PU-2can be p-type transistors while the pull-down transistors PD-1 and PD-2can be n-type transistors, and the claimed scope of the presentdisclosure is not limited in this respect.

In FIG. 1, the first inverter 102 and the second inverter 104 arecross-coupled. That is, the first inverter 102 has an input connected tothe output of the second inverter 104. Likewise, the second inverter 104has an input connected to the output of the first inverter 102. Theoutput of the first inverter 102 is referred to as a storage node 103.Likewise, the output of the second inverter 104 is referred to as astorage node 105. In a normal operating mode, the storage node 103 is inthe opposite logic state as the storage node 105. By employing the twocross-coupled inverters, the SRAM cell 100 can hold the data using alatched structure so that the stored data will not be lost withoutapplying a refresh cycle as long as power is supplied through Vdd.

In an SRAM device using the 6T SRAM cells, the cells are arranged inrows and columns. The columns of the SRAM array are formed by a bit linepairs, namely a first bit line BL and a second bit line BLB. The cellsof the SRAM device are disposed between the respective bit line pairs.As shown in FIG. 1, the SRAM cell 100 is placed between the bit line BLand the bit line BLB.

In FIG. 1, the SRAM cell 100 further includes a first pass-gatetransistor PG-1 connected between the bit line BL and the output 103 ofthe first inverter 102. The SRAM cell 100 further includes a secondpass-gate transistor PG-2 connected between the bit line BLB and theoutput 105 of the second inverter 104. The gates of the first pass-gatetransistor PG-1 and the second pass-gate transistor PG-2 are connectedto a word line WL, which connects SRAM cells in a row of the SRAM array.

In operation, if the pass-gate transistors PG-1 and PG-2 are inactive,the SRAM cell 100 will maintain the complementary values at storagenodes 103 and 105 indefinitely as long as power is provided through Vdd.This is so because each inverter of the pair of cross coupled invertersdrives the input of the other, thereby maintaining the voltages at thestorage nodes. This situation will remain stable until the power isremoved from the SRAM, or, a write cycle is performed changing thestored data at the storage nodes.

In the circuit diagram of FIG. 1, the pull-up transistors PU-1, PU-2 arep-type transistors. The pull-down transistors PD-1, PD-2, and thepass-gate transistors PG-1, PG-2 are n-type transistors. In some otherembodiments, however, the pull-up transistors PU-1, PU-2 are n-typetransistors, and the pull-down transistors PD-1, PD-2, and the pass-gatetransistors PG-1, PG-2 are p-type transistors. According to variousembodiments, the pull-up transistors PU-1, PU-2, the pull-downtransistors PD-1, PD-2, and the pass-gate transistors PG-1, PG-2 areimplemented by FinFETs.

The structure of the SRAM cell 100 in FIG. 1 is described in the contextof the 6T-SRAM. One of ordinary skill in the art, however, shouldunderstand that features of the various embodiments described herein maybe used for forming other types of devices, such as an 8T-SRAM memorydevice, or memory devices other than SRAMs, such as standard cell, gateddiode or ESD (Electrostatic Discharge) devices. Furthermore, embodimentsof the present disclosure may be used as stand-alone memory devices,memory devices integrated with other integrated circuitry, or the like.

FIGS. 2A, 3A and 4A are top views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure. FIGS. 2B, 3B, and 4B areperspective views of area B of FIGS. 2A, 3A and 4A. FIGS. 5A. 6A, 7A,8A, 9A, 10A, 11A. 12A are perspective views of area B of FIG. 4A in thefollowing processes. FIGS. 2C and 3C are cross-sectional views of lineA-A of FIGS. 2A and 3A. FIGS. 5B. 6B, 7B, 8B, 9B, 10B, 11B. 12B arecross-sectional views of line A-A of FIG. 4A in the following processes.

In FIG. 2A, the semiconductor device can be a SRAM device including fourSRAM cells 200 a, 200 b, 200 c, and 200 d. In some other embodiments,however, the number of the SRAM cells 200 a, 200 b, 200 c, and 200 d inthe SRAM device is not limited in this respect.

Reference is made to FIGS. 2A, 2B, and 2C. A substrate 210 is provided.In some embodiments, the substrate 210 may be a semiconductor materialand may include known structures including a graded layer or a buriedoxide, for example. In some embodiments, the substrate 210 includes bulksilicon that may be undoped or doped (e.g., p-type, n-type, or acombination thereof). Other materials that are suitable forsemiconductor device formation may be used. Other materials, such asgermanium, quartz, sapphire, and glass could alternatively be used forthe substrate 210. Alternatively, the silicon substrate 210 may be anactive layer of a semiconductor-on-insulator (SOI) substrate or amulti-layered structure such as a silicon-germanium layer formed on abulk silicon layer.

A plurality of p-well regions 212 and a plurality of n-well regions 216are formed in the substrate 210. One of the n-well regions 216 is formedbetween two of the p-well regions 212. The p-well regions 212 areimplanted with P dopant material, such as boron ions, and the n-wellregions 216 are implanted with N dopant material such as arsenic ions.During the implantation of the p-well regions 212, the n-well regions216 are covered with masks (such as photoresist), and duringimplantation of the n-well regions 216, the p-well regions 212 arecovered with masks (such as photoresist).

A plurality of semiconductor fins 222, 224, 226, and 228 are formed onthe substrate 210. In greater detail, the semiconductor fins 222 and 226are formed on the p-well regions 212, and the semiconductor fins 224 and228 are formed on the n-well regions 216. The semiconductor fin 222 isadjacent to the semiconductor fin 224, and the semiconductor fin 226 isadjacent to the semiconductor fin 228. In some embodiments, thesemiconductor fins 222, 224, 226, and 228 include silicon. It is notethat the number of the semiconductor fins 222, 224, 226, and 228 inFIGS. 2B and 2C is illustrative, and should not limit the claimed scopeof the present disclosure. A person having ordinary skill in the art mayselect suitable number for the semiconductor fins 222, 224, 226, and 228according to actual situations.

The semiconductor fins 222, 224, 226, and 228 may be formed, forexample, by patterning and etching the substrate 210 usingphotolithography techniques. In some embodiments, a layer of photoresistmaterial (not shown) is deposited over the substrate 210. The layer ofphotoresist material is irradiated (exposed) in accordance with adesired pattern (the semiconductor fins 222, 224, 226, and 228 in thiscase) and developed to remove a portion of the photoresist material. Theremaining photoresist material protects the underlying material fromsubsequent processing steps, such as etching. It should be noted thatother masks, such as an oxide or silicon nitride mask, may also be usedin the etching process.

Reference is made to FIGS. 3A, 3B, and 3C. A portion of thesemiconductor fins 224 and 228 are removed. For example, a photomask(not shown) containing patterns for both the semiconductor fins 224 and228 are used to protect portions of the semiconductor fins 224 and 228to be kept. Exposed portions of both the semiconductor fins 224 and 228are then etched at the same time.

A plurality of isolation structures 230 are formed on the substrate 210.The isolation structures 230 are formed between the semiconductor fins226 and 228, between the semiconductor fins 228 and 224, and between thesemiconductor fins 224 and 222. The isolation structures 230, which actas a shallow trench isolation (STI) around the semiconductor fins 222,224, 226, and 228, may be formed by chemical vapor deposition (CVD)techniques using tetra-ethyl-ortho-silicate (TEOS) and oxygen as aprecursor. In some other embodiments, the isolation structures 230 maybe formed by implanting ions, such as oxygen, nitrogen, carbon, or thelike, into the substrate 210. In yet some other embodiments, theisolation structures 230 are insulator layers of a SOI wafer.

Reference is made to FIGS. 4A, and 4B. A plurality of gate stacks 242,244, 246, and 248 are formed on portions of the semiconductor fins 222,224, 226, and 228 and expose another portions of the semiconductor fins222, 224, 226, and 228. In greater detail, the gate stack 242 is formedon portions of the semiconductor fins 222, 224, and further on a portionof the semiconductor fin 228 in some embodiments; the gate stack 244 isformed on portions of the semiconductor fins 226 and 228, and further ona portion of the semiconductor fin 224 in some embodiments; the gatestack 246 is formed on portions of the semiconductor fins 222, and thegate stack 248 is formed on portions of the semiconductor fins 226.

As shown in FIG. 4B, at least one of the gate stacks 242, 244, 246, and248 includes a gate insulator layer 240 a and a gate electrode layer 240b. The gate insulator layer 240 a is disposed between the gate electrodelayer 240 b and the substrate 210, and is formed on the semiconductorfins 222, 224, 226, and 228. The gate insulator layer 240 a, whichprevents electron depletion, may include, for example, a high-kdielectric material such as metal oxides, metal nitrides, metalsilicates, transition metal-oxides, transition metal-nitrides,transition metal-silicates, oxynitrides of metals, metal aluminates,zirconium silicate, zirconium aluminate, or combinations thereof. Someembodiments may include hafnium oxide (HfO₂), hafnium silicon oxide(HfSiO), hafnium silicon oxynitride (HfSiON), hafnium tantalum oxide(HfTaO), hafnium titanium oxide (HMO), hafnium zirconium oxide (HfZrO),lanthanum oxide (LaO), zirconium oxide (ZrO), titanium oxide (TiO),tantalum oxide (Ta₂O₅), yttrium oxide (Y₂O₃), strontium titanium oxide(SrTiO₃, STO), barium titanium oxide (BaTiO₃, BTO), barium zirconiumoxide (BaZrO), hafnium lanthanum oxide (HfLaO), lanthanum silicon oxide(LaSiO), aluminum silicon oxide (AlSiO), aluminum oxide (Al₂O₃), siliconnitride (Si₃N₄), oxynitrides (SiON), and combinations thereof. The gateinsulator layer 240 a may have a multilayer structure such as one layerof silicon oxide (e.g., interfacial layer) and another layer of high-kmaterial.

The gate insulator layer 240 a may be formed using chemical vapordeposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), thermal oxide, ozone oxidation, other suitableprocesses, or combinations thereof. The gate electrode layers 240 b areformed over the substrate 210 to cover the gate insulator layers 240 aand the portions of the semiconductor fins 222, 224, 226, and 228. Insome embodiments, the gate electrode layer 240 b includes asemiconductor material such as polysilicon, amorphous silicon, or thelike. The gate electrode layer 240 b may be deposited doped or undoped.For example, in some embodiments, the gate electrode layer 240 bincludes polysilicon deposited undoped by low-pressure chemical vapordeposition (LPCVD). The polysilicon may also be deposited, for example,by furnace deposition of an in-situ doped polysilicon. Alternatively,the gate electrode layer 240 b may include a polysilicon metal alloy ora metal gate including metals such as tungsten (W), nickel (Ni),aluminum (Al), tantalum (Ta), titanium (Ti), or any combination thereof.

In FIG. 4B, a plurality of gate spacers 250 are formed over thesubstrate 210 and along the side of the gate stacks 242, 244, 246, and248. For clarity, the gate spacers 250 are illustrated in FIG. 4B andare omitted in FIG. 4A. In some embodiments, the gate spacers 250 mayinclude silicon oxide, silicon nitride, silicon oxy-nitride, or othersuitable material. The gate spacers 250 may include a single layer ormultilayer structure. A blanket layer of the gate spacers 250 may beformed by CVD, PVD, ALD, or other suitable technique. Then, ananisotropic etching is performed on the blanket layer to form a pair ofthe gate spacers 250 on two sides of the gate stacks 242, 244, 246, and248. In some embodiments, the gate spacers 250 are used to offsetsubsequently formed doped regions, such as source/drain regions. Thegate spacers 250 may further be used for designing or modifying thesource/drain region (junction) profile.

In FIG. 4A, the semiconductor fin 222 and the gate stack 242 form apull-down transistor PD-1, and the semiconductor fin 224 and the gatestack 242 form a pull-up transistor PU-1. In other words, the pull-downtransistor PD-1 and the pull-up transistor PU-1 share the gate stack242. The semiconductor fin 226 and the gate stack 244 form anotherpull-down transistor PD-2, and the semiconductor fin 228 and the gatestack 244 form another pull-up transistor PU-2. In other words, thepull-down transistor PD-2 and the pull-up transistor PU-2 share the gatestack 244. Moreover, the semiconductor fin 222 and the gate stack 246form a pass-gate transistor PG-1. In other words, the pass-gatetransistor PG-1 and the pull-down transistor PD-1 share thesemiconductor fin 222. The semiconductor fin 226 and the gate stack 248form another pass-gate transistor PG-2. In other words, the pass-gatetransistor PG-2 and the pull-down transistor PD-2 share thesemiconductor fin 226. Therefore, the SRAM cell 200 a is asix-transistor (6T) SRAM. One of ordinary skill in the art, however,should understand that features of the various embodiments describedherein may be used for forming other types of devices, such as an8T-SRAM memory device.

In some embodiments, the number of the semiconductor fins 222 can beplural, and/or the number of the semiconductor fins 226 can be plural.Therefore, the pull-down transistors PD-1, PD-2, and the pass-gatetransistors PG-1, PG-2 have a plurality of semiconductor fins pertransistor, and the pull-up transistors PU-1 and PU-2 have onesemiconductor fin per transistor, and the claimed scope is not limitedin this respect.

In FIG. 4A, when the SRAM cells 200 a-200 d are arranged together toform an array (the SRAM device herein), the cell layouts may be flippedor rotated to enable higher packing densities. Often by flipping thecell over a cell boundary or axis and placing the flipped cell adjacentthe original cell, common nodes and connections can be combined toincrease packing density. For example, the SRAM cells 200 a-200 d aremirror images and in rotated images of each other. Specifically, theSRAM cells 200 a and 200 b are mirror images across a Y-axis, as is SRAMcells 200 c and 200 d. The SRAM cells 200 a and 200 c are mirror imagesacross an X-axis, as is SRAM cells 200 b and 200 d. Further, thediagonal SRAM cells (the SRAM cells 200 a and 200 d; the SRAM cells 200b and 200 c) are rotated images of each other at 180 degrees.

Reference is made to FIGS. 5A and 5B. A spacer layer 260 is formed overthe substrate 210, and covers the semiconductor fins 222, 224, 226, and228, and further covers the isolation structures 230. The spacer layer260 may include a dielectric material such as silicon oxide.Alternatively, the spacer layer 260 may include silicon nitride, SiC,SiON, or combinations thereof. After the spacer layer 260 is formed, adielectric layer 270 is then formed over the substrate and on the spacerlayer 260. The material of the spacer layer 260 and the dielectric layer270 may be the same or may be different in embodiments. In someembodiments, the spacer layer 260 and the dielectric layer 270 are madefrom different materials to provide etching selectivity.

The gate spacers 250 and the spacer layer 260 may be the same or may bedifferent in embodiments. In some embodiments where the gate spacers 250and the spacer layer 260 are made of the same material, the gate spacers250 and the spacer layer 260 may be formed by the same process, such asCVD, PVD, ALD, or suitable process(es). In some embodiments where thegate spacers 250 and the spacer layer 260 are made of differentmaterials, the gate spacers 250 and the spacer layer 260 are formed bydifferent processes, as described in FIGS. 4A-5B.

Reference is made to FIGS. 6A and 6B. The dielectric layer 270 in FIGS.5A and 5B is patterned to form a plurality of the dielectric materials270′ on the spacer layer 260. The dielectric layer 270 may be patternedby one or more etching process(es).

The etching process may include dry etching process, wet etchingprocess, and/or combinations thereof. The etching process may alsoinclude a selective wet etch or a selective dry etch. A wet etchingsolution includes a tetramethylammonium hydroxide (TMAH), aHF/HNO₃/CH₃COOH solution, or other suitable solution. The dry and wetetching processes have etching parameters that can be tuned, such asetchants used, etching temperature, etching solution concentration,etching pressure, source power, RF bias voltage, RF bias power, etchantflow rate, and other suitable parameters. For example, a wet etchingsolution may include NH₄OH, KOH (potassium hydroxide), HF (hydrofluoricacid), TMAH (tetramethylammonium hydroxide), other suitable wet etchingsolutions, or combinations thereof. Dry etching processes include abiased plasma etching process that uses a chlorine-based chemistry.Other dry etchant gasses include CF₄, NF₃, SF₆, and He. Dry etching mayalso be performed anisotropically using such mechanisms as DRIE (deepreactive-ion etching).

Reference is made to FIGS. 7A and 7B. The spacer layer 260 in FIGS. 6Aand 6B is patterned to form a plurality of spacers 260′. In greaterdetails, portions of the spacer layer 260 are removed, and the remainedspacers 260′ are disposed between the semiconductor fins 226 and 228,and between the semiconductor fins 222 and 224. One of the spacers 260′has a recess 262 therein. Moreover, one of the spacers 260′ is incontact with the isolation structures 230 and semiconductor fins 226 and228, and another one of the spacers 260′ is in contact with theisolation structures 230 and semiconductor fins 222 and 224. From theother view, the portions of the isolation structures 230 are disposedunder the spacers 260′ and between the semiconductor fins 222 and 224,or between the semiconductor fins 226 and 228.

The spacer layer 260 may be patterned by one or more suitable etchingprocess(es). In some embodiments, during the patterning of the spacerlayer 260, the dielectric materials 270′ (see FIGS. 6A and 6B) arepartially removed. Accordingly, the remained dielectric materials 270″are disposed respectively in the recesses 262 between the spacers 260′.In some other embodiments, the dielectric materials 270′ and the spacerlayer 260 have etching selectivity, such that the dielectric materials270′ remain during the patterning of the spacer layer 260.

Reference is made to FIGS. 8A and 8B. A mask layer 280 is formed overthe substrate 210, and covers the semiconductor fins 224 and 228. Thatis, the semiconductor fins 222 and 226 are exposed, and thesemiconductor fins 224 and 228 are protected by the mask layer 280during process(es) performed later. On the other hands, one of thespacers 260′ includes a first side 260A and a second side 260B oppositeto the first side 260A, in which the mask layer 280 covers the secondside 260B and expose the first side 260A. The mask layer 280 may beformed by one or more suitable process(es) including various deposition,photolithography, and/or etching processes.

The mask layer 280, in some embodiments, is a hard mask layer whichincludes silicon oxide. The mask layer 280, in some other embodiments,may include silicon nitride (SiN), silicon oxynitride (SiON), siliconcarbide (SiC), SiOC, spin-on glass (SOG), a low-κ film,tetraethylorthosilicate (TEOS), plasma enhanced CVD oxide (PE-oxide),high-aspect-ratio-process (HARP) formed oxide, amorphous carbonmaterial, tetraethylorthosilicate (TEOS), other suitable materials,and/or combinations thereof.

Reference is made to FIGS. 9A and 9B. A plurality of epitaxy structures292 and 296 are formed respectively on the semiconductor fins 222 and226. The epitaxy structure 292 is in contact with a sidewall 222A of thesemiconductor fin 222, and the epitaxy structure 296 is in contact witha sidewall 226A of the semiconductor fin 226, respectively. On the otherhands, another sidewall 222B opposite to the sidewall 222A is in contactwith one of the spacers 260′, and another sidewall 226B opposite to thesidewall 226A is in contact with one of the spacers 260′, respectively.Moreover, a portion of the epitaxy structure 292 extends past thesidewall 222B of the semiconductor fin 222 and disposed on the firstside 260A of the spacer 260′, and a portion of the epitaxy structure 296extends past the sidewall 226B of the semiconductor fin 226 and disposedon the first side 260A of the spacer 260′. The epitaxy structures 292and 296 are in contact with the first sides 260A of the spacers 260′.

Referring to FIG. 9B, since the spacers 260′ are formed respectively onthe sidewall 222B and the sidewall 226B, the profile of the epitaxystructures 292 and 296 are asymmetric. The profile of the epitaxystructure 292 is asymmetric with respect to the semiconductor fin 222,and profile of the epitaxy structure 296 is asymmetric with respect tothe semiconductor fin 226. In greater detail, a line 222M is defined asa middle line of the semiconductor fin 222, in which the distancebetween the line 222M and the sidewall 222A is substantially equal tothe distance between the line 222M and the sidewall 222B. The epitaxystructure 292 has a width 292A along a direction from the line 222Mtoward the sidewall 222A and a width 292B along a direction from theline 222M toward the sidewall 222B. Since the spacer 260′ limits thelateral growth of the epitaxy structure 292, the width 292B is smallerthan the width 292A. Similarly, the epitaxy structure 296 has a width296A along a direction from the line 226M toward the sidewall 226A and awidth 296B along a direction from the line 226M toward the sidewall226B, in which the width 296B is smaller than the width 296A. The term“substantially” as used herein may be applied to modify any quantitativerepresentation which could permissibly vary without resulting in achange in the basic function to which it is related.

The epitaxy structure 292 covers the sidewall 222A, and the epitaxystructure 296 covers the sidewall 226A, respectively. That is, theepitaxy structure 292 covers a sidewall of the semiconductor fin 222opposite to the semiconductor fin 224, and the epitaxy structure 296covers a sidewall of the semiconductor fin 226 opposite to thesemiconductor fin 228. Moreover, the isolation structure 230 may beseparated into a first isolation structure 232 and a second isolationstructure 234, in which the first isolation structure 232 and the secondisolation structure 234 are disposed respectively on the sidewalls 222Aand 222B of the semiconductor fin 222. In greater detail, the epitaxystructure 290 is disposed on the first isolation structure 232, and thespacer 260′ is disposed on the second isolation structure 234.

The epitaxy structures 292 and 296 may be formed using one or moreepitaxy or epitaxial (epi) processes, such that Si features, SiGefeatures, and/or other suitable features can be formed in a crystallinestate on the semiconductor fins 222 and 226. In some embodiments,lattice constants of the epitaxy structures 292 and 296 is differentfrom lattice constants of the semiconductor fins 222 and 226, and theepitaxy structures 292 and 296 is strained or stressed to enable carriermobility of the semiconductor device and enhance the device performance.The epitaxy structures 292 and 296 may include semiconductor materialsuch as germanium (Ge) or silicon (Si); or compound semiconductormaterials, such as gallium arsenide (GaAs), aluminum gallium arsenide(AlGaAs), silicon germanium (SiGe), silicon carbide (SiC), or galliumarsenide phosphide (GaAsP).

In some embodiments, the epitaxy structures 292 and 296 may include SiP,SiC, SiPC, Si, III-V compound semiconductor materials, or combinationsthereof for the n-type epitaxy structure, and the epitaxy structures 292and 296 may include SiGe, SiGeC, Ge, Si, III-V compound semiconductormaterials, or combinations thereof for the p-type epitaxy structure.During the formation of the n-type epitaxy structure, n-type impuritiessuch as phosphorous or arsenic may be doped with the proceeding of theepitaxy. For example, when the epitaxy structures 292 and 296 includeSiC or Si, n-type impurities are doped. Moreover, during the formationof the p-type epitaxy structure, p-type impurities such as boron or BF₂may be doped with the proceeding of the epitaxy. For example, when theepitaxy structures 292 and 296 include SiGe, p-type impurities aredoped. The epitaxy processes include CVD deposition techniques (e.g.,vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)),molecular beam epitaxy, and/or other suitable processes. The epitaxyprocess may use gaseous and/or liquid precursors, which interact withthe composition of the semiconductor fins 222 and 226 (e.g., silicon).Thus, a strained channel can be achieved to increase carrier mobilityand enhance device performance. The epitaxy structures 292 and 296 maybe in-situ doped. If the epitaxy structures 292 and 296 are not in-situdoped, a second implantation process (i.e., a junction implant process)is performed to dope the epitaxy structures 292 and 296. One or moreannealing processes may be performed to activate the epitaxy structures292 and 296. The annealing processes include rapid thermal annealing(RTA) and/or laser annealing processes.

Reference is made to FIGS. 10A and 10B. The mask layer 280 (see FIGS. 8Aand 8B) is removed to expose the semiconductor fins 224 and 228. Themask layer 280 may be removed by suitable process(es), such as etching.

Reference is made to FIGS. 11A and 11B. A plurality of epitaxystructures 294 and 298 are formed respectively on the semiconductor fins224 and 228. During the formation of the epitaxy structures 294 and 298,another mask layer (not shown) may be formed on the epitaxy structures292 and 296. The epitaxy structures 292, 294, 296, and 298 are separatedfrom each other. The epitaxy structure 294 is in contact with a sidewall224A of the semiconductor fin 224, and the epitaxy structure 298 is incontact with a sidewall 228A of the semiconductor fin 228, respectively.On the other hands, another sidewall 224B opposite to the sidewall 224Ais in contact with one of the spacers 260′, and another sidewall 228Bopposite to the sidewall 228A is in contact with one of the spacers260′, respectively. Moreover, a portion of the epitaxy structure 294extends past the sidewall 224B of the semiconductor fin 224 and disposedon the spacer 260′, and a portion of the epitaxy structure 298 extendspast the sidewall 228B of the semiconductor fin 228 and disposed on thespacer 260′. In some embodiments, the epitaxy structures 294 and 298 maybe p-type epitaxy structures in n-well region, and the epitaxystructures 292 and 296 may be n-type epitaxy structures in p-wellregion. Thus, one of the spacers 260′ and the dielectric material 270″are disposed between one n-type epitaxy structure and one p-type epitaxystructure, such as the epitaxy structure 292 and 294, or the epitaxystructure 296 and 298.

Referring to FIG. 11B, similar to FIG. 9B, the profile of the epitaxystructure 294 is asymmetric with respect to the semiconductor fin 224,and the profile of the epitaxy structure 298 is asymmetric with respectto the semiconductor fin 228. The epitaxy structure 294 has a width 294Aalong a direction from the line 224M toward the sidewall 224A and awidth 294B along a direction from the line 224M toward the sidewall224B. Since the spacer 260′ limits the lateral growth of the epitaxystructure 294, the width 294B is smaller than the width 294A. Similarly,the epitaxy structure 298 has a width 298A along a direction from theline 228M toward the sidewall 228A and a width 298B along a directionfrom the line 228M toward the sidewall 228B, in which the width 298B issmaller than the width 298A.

Reference is made to FIGS. 12A and 12B. An interlayer dielectric 300 isformed over the substrate 210 and at outer sides of the gate spacers250. Accordingly, the interlayer dielectric 300 covers the epitaxystructures 292, 294, 296 and 298. The interlayer dielectric 300 mayinclude silicon oxide, oxynitride or other suitable materials. Theinterlayer dielectric 300 includes a single layer or multiple layers.The interlayer dielectric 300 can be formed by a suitable technique,such as CVD or ALD. A chemical mechanical planarization (CMP) processmay be applied to remove excessive interlayer dielectric 300. Anotherrecessing process may be performed to the dielectric layer to form aplurality of openings (not shown) that expose the epitaxy structures292, 294, 296 and 298. Metal such as tungsten is then deposited into theopenings down to the epitaxy structures 292, 294, 296 and 298 to formsource/drain contacts (not shown) in the interlayer dielectric 300.

FIGS. 13 and 14 are cross-sectional views of an SRAM device inaccordance with some embodiments of the present disclosure.

Reference is made to FIG. 13. The dielectric materials 270″ (see FIGS.11A and 11B) may be removed or omitted in some embodiments. Thus, theinterlayer dielectric 300 is in contact with the surface 264 of thespacers 260′. Other relevant structural and manufacturing details of theSRAM device of FIG. 13 are similar to the SRAM device of FIG. 12B, and,therefore, a description in this regard will not be repeatedhereinafter.

Reference is made to FIG. 14. The spacers 260′ and the dielectricmaterials 270 (see FIGS. 11A and 11B) may be removed after forming theepitaxy structures 292, 294, 296, and 298 (see FIGS. 11A and 11B).Accordingly, the interlayer dielectric 300 is in contact with thesidewalls 222B, 22B, 226B, and 228B of the semiconductor fins 222, 224,226, and 228, respectively. In some embodiments, the spacers 260′ andthe dielectric materials 270 may be removed by one or more suitableprocess(es), such as etching. Other relevant structural andmanufacturing details of the SRAM device of FIG. 14 are similar to theSRAM device of FIG. 12B, and, therefore, a description in this regardwill not be repeated hereinafter.

FIGS. 15A to 15C are cross-sectional views of a method for manufacturingan SRAM device at various stages in accordance with some embodiments ofthe present disclosure.

Reference is made to FIG. 15A. After the mask layer 280 is formed (seeFIGS. 8A and 8B) to cover the semiconductor fins 224 and 228, an etchingback process is performed to the spacers 260′ to partially remove thespacers 260′ on the sidewall 222B and the sidewall 226B. Thus, aplurality of recesses 266 are formed between the semiconductor fin 222and the dielectric material 270″, and between the semiconductor fin 226and the dielectric material 270″. Accordingly, portions of the sidewall222B of the semiconductor fin 222 and portions of the sidewall 226B ofthe semiconductor fin 226 are exposed.

Reference is made to FIG. 15B. A plurality of epitaxy structures 292 and296 are formed respectively on the semiconductor fins 222 and 226. Theepitaxy structure 292 is in contact with the sidewall 222A of thesemiconductor fin 222, and the epitaxy structure 296 is in contact withthe sidewall 226A of the semiconductor fin 226, respectively. Further,due to the etching back process, the epitaxy structures 292 and 296formed respectively in the recesses 266 (see FIG. 15A). Accordingly, theepitaxy structure 292 is in contact with portions of the sidewall 222Bof the semiconductor fin 222, and the epitaxy structure 296 is incontact with portions of the sidewall 226B of the semiconductor fin 226,respectively.

Reference is made to FIG. 15C. Similar to FIG. 15B, after the epitaxystructures 292 and 296 are formed, the mask layer 280 is removed, andanother etching back process is performed to the spacers 260′ to exposeportions of the sidewall 224B of the semiconductor fin 224 and portionsof the sidewall 228B of the semiconductor fin 228. A plurality ofepitaxy structures 294 and 298 are formed respectively on thesemiconductor fins 224 and 228. The epitaxy structure 294 is in contactwith the sidewall 224A of the semiconductor fin 224, and the epitaxystructure 298 is in contact with the sidewall 228A of the semiconductorfin 228, respectively. Further, the epitaxy structure 294 is in contactwith portions of the sidewall 224B of the semiconductor fin 224, and theepitaxy structure 298 is in contact with portions of the sidewall 228Bof the semiconductor fin 228, respectively. Other relevant structuraland manufacturing details of the SRAM device of FIG. 15C are similar tothe SRAM device of FIG. 12B, and, therefore, a description in thisregard will not be repeated hereinafter.

FIGS. 16 and 17 are cross-sectional views of an SRAM device inaccordance with some embodiments of the present disclosure.

Reference is made to FIG. 16. After the spacers 260′ are formed, thesemiconductor fins 222, 224, 226, and 228 are trimmed by suitableprocess(es), such as etching. For example, after the semiconductor fin222 is trimmed, the semiconductor fin 222 includes a bottom portion 2221having a width W1 and a top portion 2222 having a width W2, in which thewidth W2 is less than the width W1. Other relevant structural andmanufacturing details of the semiconductor fins 224, 226, and 228 aresimilar to the semiconductor fin 222, and, therefore, a description inthis regard will not be repeated. Also, other relevant structural andmanufacturing details of the SRAM device of FIG. 16 are similar to theSRAM device of FIG. 12B, and, therefore, a description in this regardwill not be repeated hereinafter.

Reference is made to FIG. 17. After the spacers 260′ are formed, thesemiconductor fins 222, 224, 226, and 228 are partially removed bysuitable process(es), such as etching. As a result, for example, a topportion (not shown) of the semiconductor fin 222 is removed, and abottom portion 2221 of the semiconductor fin 222 remains in theisolation structures 230. Thus, an epitaxy structure 292 is formed onthe bottom portion 2221 of the semiconductor fin 222, and the epitaxystructure 292 has a sidewall 2921 in contact with a spacer 260′. In someembodiments, a bottom surface 292S of the epitaxy structure 292 and abottom surface 260S of the spacer 260′ are substantially coplanar. Thetop surface 230S of the isolation structures 230 and the top surface topsurface 2221S of the bottom portion 2221 of the semiconductor fin 222are substantially coplanar. Moreover, the bottom surface 292S of theepitaxy structure 292 is in contact with the top surface 2221S of thebottom portion 2221 of the semiconductor fin 222. Other relevantstructural and manufacturing details of the semiconductor fins 224, 226,and 228 are similar to the semiconductor fin 222, and, therefore, adescription in this regard will not be repeated. Also, other relevantstructural and manufacturing details of the SRAM device of FIG. 17 aresimilar to the SRAM device of FIG. 12B, and, therefore, a description inthis regard will not be repeated hereinafter.

FIGS. 18A to 18C are cross-sectional views of a method for manufacturingan SRAM device at various stages in accordance with some embodiments ofthe present disclosure.

Reference is made to FIG. 18A. A plurality of semiconductor fins 222,224, 226, and 228 are formed on a substrate 210. The semiconductor fins222 and 224 have a distance D1 therebetween, the semiconductor fins 224and 228 have a distance D2 therebetween, and the semiconductor fins 228and 226 have a distance D3 therebetween, in which the distances D1 andD3 are less than the distance D2.

A spacer layer 310 is formed over the substrate 210. In someembodiments, due to the small distances between the semiconductor fins,such as the distances D1 and D3, the spacer layer 310 may be mergedbetween the semiconductor fins 222 and 224, and between thesemiconductor fins 222 and 224.

Reference is made to FIG. 18B. The spacer layer 310 (see FIG. 18A) ispatterned to form a plurality of spacers 310. In some embodiments, a topsurface 310S of the spacers 310′, a top surface 222S of thesemiconductor fin 222, and a top surface 224S of the semiconductor fin224 are substantially coplanar. Other relevant structural andmanufacturing details of the spacers 310′ between the semiconductor fins226, and 228 are similar, and, therefore, a description in this regardwill not be repeated.

Reference is made to FIG. 18C. A plurality of epitaxy structures 292,294, 296, and 298 are formed respectively on the semiconductor fins 222,224, 226, and 228. The formation of the epitaxy structures 292, 294,296, and 298 is similar to the method shown in FIGS. 7A to 11A, and,therefore, a description in this regard will not be repeated. Otherrelevant structural and manufacturing details of the SRAM device of FIG.18C are similar to the SRAM device of FIG. 12B, and, therefore, adescription in this regard will not be repeated hereinafter.

FIG. 19 is cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure. Two p-well regions 212and one n-well region 216 are formed in the substrate 210. In someembodiments, the p-well regions 212 and the n-well region 216 may beplural, as described in FIG. 2A. The n-well region 216 is formed betweentwo p-well regions 212.

A plurality of semiconductor fins 222, 224, 226, and 228 are formed on asubstrate 210, in which the semiconductor fins 224 and 228 are formed inthe n-well region 216, and the semiconductor fins 222 and 226 are formedrespectively in the p-well regions 212. A plurality of spacers 264 anddielectric materials 274 are formed over the substrate 210 and betweenat least two semiconductor fins. For example, in FIG. 19, one of thespacers 264 and dielectric materials 274 are formed betweensemiconductor fins 224 and 228 in the n-well region 216.

A plurality of epitaxy structures 292, 294, 296, and 296 are formedrespectively on the semiconductor fins 222, 224, 226, and 228. Theepitaxy structures 224 and 228 may be p-type epitaxy structures in then-well region 216, and the epitaxy structures 222 and 226 may be n-typeepitaxy structures in the p-well regions 212. Accordingly, at least oneof the spacers 264 and dielectric materials 274 are formed between twop-type epitaxy structures, such as the epitaxy structures 224 and 228.In some embodiments, the at least one of the spacers 264 and dielectricmaterials 274 are formed between two n-type epitaxy structures. Otherrelevant structural and manufacturing details of the SRAM device of FIG.19 are similar to the SRAM device of FIG. 12B, and, therefore, adescription in this regard will not be repeated hereinafter.

According to the aforementioned embodiments, a spacer is formed betweenthe semiconductor fins, such that epitaxy structures formed on thesemiconductor fins may be formed asymmetrically with respect to thesemiconductor fins. One side of a width of the epitaxy structures may bereduced due to the confinement of the spacer. Thus, a distance betweenthe semiconductor fins may be reduced while the adjacent epitaxystructures are separated from each other, and the device may scale downaccordingly. With this configuration, the performance of thesemiconductor device can be improved.

According to some embodiments, a semiconductor device includes asubstrate having a semiconductor fin, in which the semiconductor fin hasa first sidewall and a second sidewall opposite to the first sidewall;an epitaxy structure in contact with the first sidewall of thesemiconductor fin; and a spacer in contact with the second sidewall ofthe semiconductor fin and the epitaxy structure.

According to some embodiments, a semiconductor device includes asubstrate having a first semiconductor fin and a second semiconductorfin adjacent to the first semiconductor fin; a first epitaxy structuredisposed on the first semiconductor fin, in which a profile of the firstepitaxy structure is asymmetric with respect to the first semiconductorfin; and a second epitaxy structure disposed on the second semiconductorfin, in which a profile of the second epitaxy structure is asymmetricwith respect to the second semiconductor fin, and the first epitaxystructure is separated from the second epitaxy structure.

According to some embodiments, a method for manufacturing asemiconductor device includes forming a first semiconductor fin and asecond semiconductor fin on a substrate; forming an isolation structureon the substrate and between the first semiconductor fin and the secondsemiconductor fin; forming a spacer layer on the first semiconductorfin, the second semiconductor fin, and the isolation structure;patterning the spacer layer to form a spacer between the firstsemiconductor fin and the second semiconductor fin; forming a firstepitaxy structure on the first semiconductor fin and at a first side ofthe spacer; and forming a second epitaxy structure on the secondsemiconductor fin and at a second side of the spacer opposite to thefirst side of the spacer, in which the spacer is in contact with thefirst epitaxy structure and the second epitaxy structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a substratehaving a first semiconductor fin and a second semiconductor fin, whereinthe first semiconductor fin has a first sidewall farthest from thesecond semiconductor fin and a second sidewall closest to the secondsemiconductor fin, and the second semiconductor fin has a third sidewallclosest to the first semiconductor fin; a shallow trench isolation (STI)structure around a lower part of the first semiconductor fin and a lowerpart of the second semiconductor fin; a fin spacer having a firstportion laterally extending along a top surface of the STI structure, asecond portion extending upwardly from the first portion of the finspacer along the second sidewall of the first semiconductor fin, and athird portion expending upwardly from the first portion along the thirdsidewall of the second semiconductor fin; and an epitaxy structure overthe first semiconductor fin and the second portion of the fin spacer,the epitaxy structure having an asymmetrical cross-section that extendsdifferently beyond the first sidewall and second sidewall of the firstsemiconductor fin, respectively.
 2. The semiconductor device of claim 1,wherein a portion of the epitaxy structure extends past the secondsidewall of the first semiconductor fin.
 3. The semiconductor device ofclaim 1, wherein the epitaxy structure is further in contact with thesecond sidewall of the first semiconductor fin.
 4. The semiconductordevice of claim 1, wherein the first semiconductor fin comprises: abottom portion having a first width; and a top portion disposed betweenthe epitaxy structure and the bottom portion, and the top portion havinga second width less than the first width.
 5. A semiconductor device,comprising: a substrate having a first semiconductor fin and a secondsemiconductor fin adjacent to the first semiconductor fin; a firstepitaxy structure disposed on the first semiconductor fin, wherein aprofile of the first epitaxy structure is asymmetric with respect to thefirst semiconductor fin; a second epitaxy structure disposed on thesecond semiconductor fin, wherein a profile of the second epitaxystructure is asymmetric with respect to the second semiconductor fin,and the first epitaxy structure is separated from the second epitaxystructure; and an shallow trench isolation (STI) structure around alower part of the first semiconductor fin and a lower part of the secondsemiconductor fin; a spacer layer forming an U-shaped pattern whenviewed in a cross-section taken along a direction perpendicular tolongitudinal axes of the first and second semiconductor fins, whereinthe U-shaped pattern lines sidewalls of the first and secondsemiconductor fins and a top surface of the STI structure, and has topends respectively capped by the first and second epitaxy structures. 6.The semiconductor device of claim 5, wherein the spacer layer is incontact with the first semiconductor fin and the second semiconductorfin.
 7. The semiconductor device of claim 5, wherein the spacer layerhas a recess therein, and the semiconductor device further comprises adielectric material disposed in the recess of the spacer layer.
 8. Thesemiconductor device of claim 5, wherein a bottom surface of the firstepitaxy structure and a bottom surface of the spacer layer aresubstantially at the same level.
 9. The semiconductor device of claim 5,wherein: the first epitaxy structure covers a sidewall of the firstsemiconductor fin opposite to the second semiconductor fin; and thesecond epitaxy structure covers a sidewall of the second semiconductorfin opposite to the first semiconductor fin.
 10. A semiconductor device,comprising: a substrate comprising a first semiconductor fin and asecond semiconductor fin, wherein the first semiconductor fin comprisesa first sidewall distal to the second semiconductor fin and a secondsidewall facing the second semiconductor fin, and the secondsemiconductor fin has a third sidewall facing the first semiconductorfin; a shallow trench isolation (STI) structure around a lower part ofthe first semiconductor fin and a lower part of the second semiconductorfin; a spacer layer lining the first sidewall of the first semiconductorfin, a top surface of the STI structure, and the third sidewall of thesecond semiconductor fin; an epitaxy structure having a first portionextending from a top surface of the first semiconductor fin to beyondthe first sidewall of the first semiconductor fin, and a second portionextending from the top surface of the first semiconductor fin to a topend of the spacer layer, the first portion and the second portionforming an asymmetrical pattern when viewed in a cross-section takenalong longitudinal axes of the first and second semiconductor fins; aspacer layer abutting the first sidewall of the first semiconductor fin,wherein the second sidewall of the first semiconductor fin is free fromcoverage of the spacer layer; and a gate stack over the substrate andcrossing the first semiconductor fin and the second semiconductor fin.11. The semiconductor of claim 10, further comprising a dielectricmaterial in contact with the spacer layer, wherein a top surface of thedielectric material is lower than a top surface of the semiconductor finand a top surface of the space layer.
 12. The semiconductor of claim 10,further comprising a dielectric material in contact with the spacerlayer, wherein a top surface of the dielectric material is lower than atop surface of the semiconductor fin and higher than a top surface ofthe space layer.
 13. The semiconductor of claim 10, wherein an interfacebetween the epitaxy structure and the spacer layer is substantiallylevel with a top surface of the first semiconductor fin.
 14. Thesemiconductor of claim 10, wherein an interface between the epitaxystructure and the spacer layer is lower than a top surface of the firstsemiconductor fin.
 15. The semiconductor device of claim 1, wherein theepitaxy structure is in contact with a top surface of the semiconductorfin.
 16. The semiconductor device of claim 1, further comprising adielectric material over the fin spacer.
 17. The semiconductor device ofclaim 16, wherein the dielectric material is separated from the firstsemiconductor fin and the second semiconductor fin.
 18. Thesemiconductor device of claim 16, wherein the dielectric material has alinear shape cross-section.
 19. The semiconductor device of claim 16,wherein a topmost surface of the dielectric material is lower than atopmost surface of the fin spacer.
 20. The semiconductor device of claim16, wherein a topmost surface of the dielectric material is higher thana topmost surface of the fin spacer.